The present invention relates generally to hydroelectric turbine installations. More particularly, this invention pertains to hydroelectric installations with means for enhancing the level of dissolved gas in water passing through the turbine.
A significant environmental problem for many hydroelectric facilities is the water quality of turbine discharges. The primary water quality problem is often low dissolved oxygen (DO) levels which occur seasonally. During the summer months, thermal stratification of the reservoir produces a surface layer of less dense, warm water with relatively high dissolved oxygen and a lower, relatively cold oxygen-depleted layer resulting from the decay of organic material on the reservoir bottom. Hydraulic turbines draw their discharges from the lower level which can create water quality problems downstream of the facility.
Relicensing and rehabilitation of a hydroelectric facility offer an opportunity to address environmental and industrial development concerns over dissolved oxygen levels and other water quality regulations which affect hydropower releases. Rehabilitating an existing hydroelectric facility may include replacement of the runner. Replacing an existing runner with a new runner having integral passages, and providing air through existing structures or new structures of the installation to the integral passages, enhances dissolved oxygen levels in the water without material losses in efficiency or substantial increases in cost of rehabilitation.
Various attempts have been made to enhance the level of dissolved oxygen in water downstream of hydroelectric installations. For example, U.S. Pat. No. 4,789,051 to Fisher, Jr. discloses an apparatus comprising a manifold which contains a bounded air channel extending the length of the runner blade trailing edge. A plurality of holes are formed along the manifold extending between the channel and the turbine interior, the channel being in fluid communication with a source of oxygen. For the manifold to remain securely fastened over extended periods of operation, the trailing edge of the runner blade must be relatively thick, which may result in efficiency losses. Additionally, many installations have existing structures which make it impractical and thereby costly to provide air directly to the trailing edge of the runner blade.
Runner blade construction consists of either a solid casting or a fabrication. Most Francis runner blades built in the 70""s and 80""s were solid cast with extra material added in critical areas for final finishing. These castings were, and often still are, hand ground to templates and fixtures to meet the desired shapes. As machine tools have improved and the runner blade designs have become more computerized, critical areas and features of more complex geometries, such as integral passages, can nowadays be machined into the cast blades. However, this ore modern machining approach has done little to improve the manufacturing cycle time, due to the long lead time associated with cast components, nor has it materially reduced manufacturing costs. Although fabricated blades offer improved cycle time and cost advantages, it has proven difficult in practice to fabricate blades having complex geometric features such as integral gas channels, particularly in the thinner portions of the blade.
The foregoing therefore indicates that prior art methods of feeding air directly to the trailing edge of the runner blade have not proved fully satisfactory in practice. Additionally, there is a need for a method of forming a runner blade having a gas channel of relatively complex geometry which offers improved cycle time and is less expensive than the prior art methods.
The present invention enhances the level of dissolved gas in water flowing through an adjustable blade turbine installation comprising a turbine runner having a hollow hub and a plurality of variable pitch blades. The hollow hub includes a first gas passage extending therethrough, the first gas passage being fluidly coupled to a gas source. The plurality of variable pitch blades project generally radially outwardly from the outer surface of the hub. Each blade is bounded by an inner edge and a distal outer edge, and a leading edge and an opposed trailing edge separated from the leading edge by a water directing surface. The inner edge of each blade generally sweeps a region of the outer surface of the hub during variations in pitch of the blades. At least one of the blades has a second gas passage extending therethrough. The second gas passage in the blade is fluidly coupled to the first gas passage in the hub. An electrical control system controls the pitch of the at least one of the blades and regulates a flow of gas from the gas source to the first and second gas passages.
According to another aspect of the present invention, a hydraulic turbine installation is of the type including features to increase the dissolved oxygen level in water flowing through the turbine. The installation comprises a water passageway for containing turbine components and extending from an upper elevation source of water to a lower elevation discharge region. A turbine runner is disposed in the passageway so that water flowing therethrough impinges on the runner. The runner includes a hollow hub having spaced apart inner and outer surfaces and a first gas passage extending therethrough. The runner also includes a plurality of variable pitch blades projecting generally radially outwardly from the outer surface of the hub. Each blade is bounded by an inner edge and a distal outer edge, a leading edge and an opposed trailing edge separated from the leading edge by a water directing surface. The inner edge of each blade generally sweeps a region of the outer surface of the hub during variations in pitch of the blades. At least one of the blades has a second gas passage extending therethrough to a gas discharge aperture. The second gas passage in the blade is fluidly coupled to the first gas passage in the hub. An oxygen containing gas source is fluidly coupled to the first gas passage in the hub for supplying a flow of oxygen containing gas to the at least one of the blades. An electrical control system controls the pitch of the at least one of the blades and regulates a flow of oxygen containing gas to thereby regulate the dissolved oxygen level in the water.
According to a further aspect of the invention, a hydraulic turbine installation comprises a hollow hub and a plurality of variable pitch projecting generally radially outwardly therefrom at radially spaced locations. The hollow hub has a first gas passage extending therethrough, the first gas passage being fluidly coupled to a gas source. Each blade is bounded by an inner edge and a distal outer edge, and a leading edge and an opposed trailing edge separated from the leading edge by a water directing surface. The inner edge of each blade generally sweeps a region of the outer surface of the hub during variations in pitch of the blades. At least one of the blades has a second gas passage extending therethrough from a root region of the blade to a spaced apart gas discharge aperture. The at least one of the blades is pivotally mounted in the hub by a blade support assembly. The blade support assembly includes a third gas passage which fluidly couples the first gas passage in the hub to the second gas passage in the at least one of the blades. An electrical control system controls the pitch of the at least one of the blades and regulates a flow of gas from the gas source to the gas discharge aperture.
Other advantages of the invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific embodiments are given by way of illustration only since, from this detailed description, various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.